High volume flat rolled mill products made from such metals as steel, aluminum and the like are rolled down to plate sheet or strip sizes in large high capacity highly instrumented mills. In state of the art mills, the edge to edge width of metal lengths are measured as they move over table rolls adjacent to the mills in order to improve the yield and quality of the mill products while maintaining high mill utilization rates. See, e.g., U.S. Pat. No. 4,528,756 entitled "System For Detecting Camber of Rolled Material" and U.S. Pat. No. 4,672,830 entitled "Method of Controlling An Edging Opening In a Rolling Mill", which are both incorporated by this reference for their disclosures of rolling processes and mills utilizing width controls to obtain these advantages. See, also, U.S. Pat. No. 4,538,669 entitled "Distortion Measurement In Casting" which is incorporated by reference for its disclosure of width measuring devices for measuring one or more widthwise dimensions of moving metal lengths and then controlling a process variable in response to the measured width(s).
A workpiece to be rolled on modern mills is normally transferred toward each mill stand by horizontal table rolls and guided by a pair of retractable generally horizontal sideguards extending perpendicularly of the axes of the table rolls. Two modes of operation of the sideguards are used in hot strip mills. In the first mode of operation, the workpiece is stopped between sideguards prior to entering the mill stand by halting rotation of the table rolls. The sideguards are then moved inwardly against the workpiece to orient the workpiece in the direction parallel to the mill stand pass line and to locate the workpiece in the center of the mill stand. Then, the sideguards are retracted to about 0.5 inch (10 millimeters) from each edge of the workpiece and the workpiece is transferred into the mill stand roll bite by rotating the table rolls. In the second mode of operation, the workpiece is not stopped prior to entering the mill. In that case, the sideguards are maintained open about 0.5 inch (10 millimeters) from each edge of the workpiece.
The various control systems must be immediately operational or the initially rolled metal may not meet product specifications. Most desirably the means for measuring the width of a workpiece is operational at all times. Accordingly, there is a constant need for a better means for measuring the edge to edge widths of moving workpieces as they are being flat rolled. From a yield and quality viewpoint, it is also desirable that the measuring means does not damage the edges of the metal. From an operating viewpoint, it is also desirable that the measuring means be safe, be rugged and yet not be subject to excessive wear and tear throughout a large temperature range, be as compatible as possible with normally available plant utilities such as electrical power, air and the like, and not be too costly.